1. Field of the Invention
The present invention relates to a mobile tracking system for QoS guaranteed paths, a router device used for this system, a mobile communications terminal, and a control program for controlling a router device. More particularly, it relates to a communications system which transfers packets to/from a mobile communications terminal via QoS guaranteed paths, a router device used for this system, a mobile communications terminal, and a control program for controlling the router device.
2. Description of the Related Art
Known technologies intended to provide high-quality services on communications networks such as the Internet include MPLS (Multi-protocol Label Switching) and RSVP (Resource Reservation Protocol) which set up a QoS (Quality of Service) guaranteed path with a guaranteed band width between communications terminals. MPLS is described, for example, in a document by B. Jamoussi, et al. “Constraint-Based LSP Setup using LDP,” Internet-draft, draft-ietf-mpls-cr-ldp-06.txt, November 2001 (hereinafter referred to as document 1) and a document by D. O. Awduche, et al. “RSVP-TE: Extensions to RSVP for LSP Tunnels,” Internet-draft, draft-ietf-mpls-rsvp-lsp-tunnel-09.txt, August 2001 (hereinafter referred to as document 2).
Also, RSVP is described, for example, in a document by R. Braden, et al. “Resource ReSerVation Protocol (RSVP),” RFC2205, September 1997 (hereinafter referred to as document 3).
On the other hand, known technologies intended to provide packet reachability to mobile communications terminals on communications networks include for example Mobile IP. Mobile IP is described in a document by C. Perkins “IP Mobility Support,” RFC2202, Octtober 1996 (hereinafter referred to as document 4) and a document by D. B. Johnson, et al. “Mobility Support in IPv6,” Internet-draft, draft-ietf-mobileip-ipv6-15.txt, July 2001 (hereinafter referred to as document 5).
However, MPLS (documents 1 and 2) and RSVP (document 3), which are intended for use on fixed networks, are not capable of tracking a QoS guaranteed path when communications terminals are mobile. Also, Mobile IP (documents 4 and 5), which provides only packet reachability to mobile communications terminals, is not capable of packet transfer with QoS guarantees.
Known technologies for solving this problem includes a mobile tracking system for QoS guaranteed paths which is intended to provide both QoS guarantees for packet transfer according to MPLS and packet reachability according to Mobile IP. This is described in a document by J. K. Choi, et al. “Mobile IPv6 support in MPLS Network,” Internet-draft, draft-choi-mobileip-ipv6-mpls-01.txt, August 2001 (hereinafter referred to as document 6).
Problems with the conventional mobile tracking system for QoS guaranteed paths described in document 6 will be described with reference to FIGS. 15 and 16.
First, suppose a communications network 100 comprises edge routers ER1 to ER 3 and core routers CR1 and CR2, as shown in FIG. 15. Also, let's assume that a mobile communications terminal 200 is conducting packet transmission with a remote terminal 300 (corresponding terminal) via this network 100.
In this active state of communication, if the mobile communications terminal 200 moves from its original position in an old visitor location area A1 to an area A12 in which the coverage area of the edge router ER1 and the coverage area of the edge router ER2 overlap, operations such as those shown in a sequence diagram in FIG. 16 are carried out.
In FIG. 16, when a packet S1 is transmitted between the mobile communications terminal 200 and remote terminal 300 via an existing QoS guaranteed path P0, if information S2 about a new visitor location address (router advertisement) is received from the edge router ER2 which belongs to a new visitor location area A2, the mobile communications terminal 200 transfers an upstream packet S3 containing a location registration update request (binding update) and desired QoS parameter to the remote terminal 300 using the new address.
The packet S3 received by the edge router ER2 which belongs to the new visitor location area A2 is transferred on a best-effort basis via a path without a QoS guarantee until a new QoS guaranteed path has been set up. Meanwhile, the edge router ER2 which belongs to the new visitor location area A2 sends out a new-QoS-guaranteed-path setup request S4 to the edge router ER3 on the side of the remote terminal 300 and starts setting up a new QoS guaranteed path.
Upon receiving the packet S3 containing a location registration update request and QoS parameter from the mobile communications terminal 200, the remote terminal 300 updates its own table containing correspondence between the address unique to the mobile communications terminal 200 and visitor location address. This enables a downstream packet S6 to be transferred to the new visitor location address via a path between the edge router ER2 and edge router ER3.
At this time, if the edge router ER2 which belongs to the new visitor location area has received a new-QoS-guaranteed-path setup acknowledgment S5 from the edge router ER3 on the side of the remote terminal 300, packet transfer can be performed via a new QoS guaranteed path P1. However, if the edge router ER2 which belongs to the new visitor location area has not received a new-QoS-guaranteed-path setup acknowledgment S5 from the edge router ER3 on the side of the remote terminal 300, the packet transfer to the new visitor location address of the mobile communications terminal 200 is performed on a best-effort basis without a QoS guarantee.
That is, in the system shown in FIG. 15, upstream packets are transferred on a best-effort basis until a new QoS guaranteed path has been set up. On the other hand, downstream packets are transferred via an existing path with QoS guarantees until a location registration update request signal is received. After a location registration update request signal is received, they are transferred on a best-effort basis until a new QoS guaranteed path has been set up.
Thus, the conventional mobile tracking system for QoS guaranteed paths has the problem that it cannot control upstream and downstream packet transfer paths and cannot always transfer packets with QoS guarantees.
Also, the conventional system has the problem that it cannot setup a new QoS guaranteed path correctly when terminals communicating with each other move simultaneously. This problem will be described with reference to FIGS. 17 and 18. FIG. 17 is a block diagram illustrating this problem, wherein components equivalent to those in FIG. 15 are denoted by the same reference numerals/characters as corresponding components in FIG. 15.
In FIG. 17, let's assume that the mobile communications terminal 200 moves from the visitor location area A1 of the edge router ER1 to the new visitor location area A2 of the edge router ER2. In relation to this movement, the edge router ER2 sets up a new QoS guaranteed path toward the edge router ER3.
Almost simultaneously with the movement of the mobile communications terminal 200, a mobile communications terminal 400 moves from a visitor location area B1 of the edge router ER3 to a new visitor location area B2 of an edge router ER4. Then, an edge router ER4 sets up a new QoS guaranteed path toward the edge router ER1.
When new QoS guaranteed paths are set up almost simultaneously as described above, operations shown in a sequence diagram in FIG. 18 are carried out.
In FIG. 18, when a packet S1 is transmitted between the mobile communications terminal 200 and mobile communications terminal 400 via an existing QoS guaranteed path P0, if information S2 about a new visitor location address is received from the edge router ER2 which belongs to a new visitor location area A2, the mobile communications terminal 200 transfers an upstream packet S3 containing a location registration update request and desired QoS parameter to the mobile communications terminal 400 using the new address. The packet S3 received by the edge router ER2 which belongs to the new visitor location area A2 is transferred on a best-effort basis via a path without a QoS guarantee until a new QoS guaranteed path has been set up. Meanwhile, the edge router ER2 which belongs to the new visitor location area A2 sends out a new-QoS-guaranteed-path setup request S4 to the edge router ER3 on the side of the mobile communications terminal 400 and starts setting up a new QoS guaranteed path.
Almost simultaneously with the movement of the mobile communications terminal 200, if information S2′ about a new visitor location address is received from the edge router ER4 which belongs to the new visitor location area B2, the mobile communications terminal 400 transfers an upstream packet S3′ containing a location registration update request and desired QoS parameter to the mobile communications terminal 200 using the new address. The packet S3′ received by the edge router ER4 which belongs to the new visitor location area B2 is transferred on a best-effort basis via a path without a QoS guarantee until a new QoS guaranteed path has been set up. Meanwhile, the edge router ER4 which belongs to the new visitor location area B2 sends out a new-QoS-guaranteed-path setup request S4′ to the edge router ER1 on the side of the mobile communications terminal 200 and starts setting up a new QoS guaranteed path.
Subsequently, if the edge router ER2 which belongs to the new visitor location area of the mobile communications terminal 200 has received a new-QoS-guaranteed-path setup acknowledgment S5 from the edge router ER3 on the side of the mobile communications terminal 400, a new QoS guaranteed path P1 will be set up. On the other hand, if the edge router ER4 which belongs to the new visitor location area of the mobile communications terminal 400 has received a new-QoS-guaranteed-path setup acknowledgment S5′ from the edge router ER1 on the side of the mobile communications terminal 200, a new QoS guaranteed path P1′ will be set up. In short, the QoS guaranteed path P1 is set up between the edge router ER2 and edge router ER3 while the other QoS guaranteed path P1′ is set up between the edge router ER1 and edge router ER4.
As described above, there is the problem that when terminals communicating with each other move simultaneously, a new QoS guaranteed path cannot be set up between the edge router ER2 and edge router ER4.
The present invention has been made to solve the above prior art problems. Its object is to provide a mobile tracking system for QoS guaranteed paths which can always guarantee QoS and can achieve continuity of QoS guaranteed paths for upstream and downstream packet transfers, a router device used for this system, a mobile communications terminal, and a control program for controlling the router device.